Wet weather increases risk of potato tuber blight

The effect of the rain on disease levels and soil conditions was an obvious concern at the East Anglian Potato Event last week. Louise Impey reports

Potato tuber blight risk has been significantly increased by the wet conditions in August, SCRI’s David Cooke said at the East Anglian Potato Event last week.

But the rapid pace of changing blight populations meant it was difficult to predict how the new, dominant genotype would behave in store, he added.

“In general, blight has been more manageable this year than last. But things are hotting up now, especially in Scotland.”

Tuber blight risk will be higher this season, says SCRI’s David Cooke

The dramatic increase in the A2 type had continued into 2008, with 80% of outbreaks having A2 in them.

“Blue” genotype 13, an A2 strain, was the dominant form of blight now found in the UK, he said. “We know a bit about blue A2, but there are still many unanswered questions.”

As it sporulates at 13C, a lower temperature than other blight strains, it can be more aggressive. “More spores are produced in a faster time, so it’s capable of producing much more blight. But we don’t know how active it will be in storage conditions. That needs to be looked at in future research.”

Other areas of uncertainty include blight prediction. “Smith periods may not be relevant if the new genotypes we’re finding are active at different temperatures and relative humidities. It’s vital to be able to predict when the disease is active, especially if we are dealing with a more aggressive strain.”

Varietal resistance to blight is also under pressure with blue A2. “We know that varieties previously considered resistant to blight – for example, Lady Balfour – are breaking down to this genotype.”

* For more information on tuber blight, refer to “Dealing with blight risk in store”, which can be found on the Potato Council website www.potato.org.uk

Tubers in store

The problem with tuber blight is you often don’t see it until the tubers are in store, Rob Clayton of Potato Council told Farmers Weekly.

Growers who had crops with a canopy that was still green, were growing a susceptible variety or targeting long-term higher temperature storage needed to make a robust assessment of risk, he said.

“Then it’s a matter of following existing best practice. That means getting crops dried and cooled as quickly as possible.”

There were plenty of theories on grading things out, Dr Clayton said. “But moving tubers spreads the risk. Try to do as little handling as possible.”

Where still relevant, blight programmes should continue until there was no green foliage left at all, he said.